In recent years, in radio communication, particularly in mobile communication, various kinds of information such as images and data other than speech have become targets of transmission. Demand for higher-speed transmission is likely to increase in the future, and, to realize high-speed transmission, a radio transmission technique is desired that realizes high transmission efficiency by utilizing limited frequency resources efficiently.
Radio transmission techniques that respond to this demand include OFDM. OFDM refers to a multicarrier transmission technique for transmitting data in parallel using a large number of subcarriers, and is known as a technique that has high frequency utilization efficiency and characteristics of reducing inter-symbol interference under a multipath environment and that is effective in improving transmission efficiency.
A technique is studied of performing frequency scheduling when this OFDM is used in downlink and data for a plurality of mobile stations is frequency-multiplexed on a plurality of subcarriers (for example, see Non-Patent Document 1).
With frequency scheduling, a base station allocates subcarriers to mobile stations adaptively based on received quality of each frequency band at the mobile stations, so that it is possible to obtain a maximal multi-user diversity effect and perform communication very efficiently.
Data for the mobile stations for which allocation is determined by frequency scheduling (for example, speech, data and image) is transmitted using a shared channel. Further, a technique is studied of reporting in a shared control channel (hereinafter “SCCH”) per mobile station, transmission parameters (for example, allocation RB [Resource Block] number, allocated mobile station ID and MCS [Modulation and Coding Scheme]) for data transmitted using a shared channel (see Non-Patent Document 1).
Non-Patent Document 1: R1-050590, “Physical Channels and Multiplexing in Evolved UTRA Downlink”, NTT DoCoMo, 3GPP TSG-RAN WG1, 2005/06